The present invention relates to a magnetoelectric transducer such as a Hall device or magnetoresistor, and more particularly to a magnetoelectric transducer using a thin film of semiconductor crystal.
Conventional magnetoelectric transducers use thin semiconductor films of InSb (indium-antimony), InAs (Indium-arsenic) and GaAs (gallium-arsenic), which are produced by vacuum vapor deposition and CVD techniques.
FIG. 1 shows a cross section of a Hall device having a thin semiconductor film formed on a ceramic substrate by vacuum vapor deposition. In FIG. 1, numeral 1 indicates the ceramic substrate, and 2 is a thin film of crystalline InSb grown by vacuum vapor deposition. An aluminum electrode layer 3 is formed on the substrate and part of the semiconductor film by vapor deposition. An aluminum oxide (Al.sub.2 O.sub.3) protective film 4 is formed on the bare part of the semiconductor film not covered by the electrode layer. The protective film extends to cover part of the electrode layer. The entire assembly is packaged within a molding resin 5 to provide a Hall device as shown in FIG. 1.
FIG. 2 is a cross section of a Hall device using a ferrite substrate 1. An aluminum oxide (Al.sub.2 O.sub.3) film 6 is deposited on the entire surface of the substrate, and a thin film of crystalline InSb 2 is formed on part of the oxide film by vacuum vapor deposition. Subsequently, as in the fabrication of the Hall device of FIG. 1, an aluminum electrode layer 3 and an Al.sub.2 O.sub.3 protective film 4 are successively formed. A collector 7 is fixed to a generally central part of the protective film on the thin semiconductor film not covered by the electrode layer. Thereafter, the entire assembly is packaged within a molding resin 5.
In the fabrication of the Hall device of FIG. 1, the surface of the partially grown crystal of InSb is mirror-polished before further growth of the crystalline semiconductor film is performed by CVD or vacuum vapor deposition techniques. Thereafter, a magnetic sensitive pattern is formed either by photoetching or mask vapor deposition effected simultaneously with the epitaxial growth. The pattern for the Al electrode layer 3 and Al.sub.2 O.sub.3 protective film 4 is also formed by photoetching or mask vapor depositions. After forming the respective layers, the devices on the substrate are cut apart and subjected to the final assembly process.
The device of FIG. 2 using a ferrite substrate can be fabricated by substantially the same method used for producing the device of FIG. 1, except that the Al.sub.2 O.sub.3 film 6 is formed on the ferrite substrate to promote crystal growth of the thin semiconductor film 2, and the collector 7 is fixed to the semiconductor film through the Al.sub.2 O.sub.3 protective film 4 so as to provide higher sensitivity.
The thin semiconductor film used as a magnetoelectric transducer is required to have a high mobility and Hall constant. With a Hall device, high product sensitivity requires a high Hall constant, and if both the Hall constant and the mobility are high, the sensitivity at maximum magnetic flux density, the Hall output and the magnetoelectric conversion efficiency increase. With a magnetoresistor, high mobilities are required to attain a great change in resistance, and if the Hall constant is also high, higher square-sensitivity and linear sensitivity can be attained.
The thin semiconductor films used as magnetoelectric transducers are commonly made of InSb and GaAs. An InSb film 1.4.mu. thick formed on a silicon substrate has a Hall constant of 200-250 cm.sup.3 /coulomb and a mobility of about 20,000 cm.sup.2 /V. sec. The mobility is very great but the Hall constant is low. Under the same conditions, a GaAs film has a Hall constant of 3,000 cm.sup.3 /coulomb and a mobility of about 4,000 cm.sup.2 /V. sec. The Hall constant is great but the mobility is small. Therefore, neither semiconductor has been able to provide a device that satisfies all the necessary characteristics.